In recent years, much progress in interactive surgical navigation has taken place. Use of mechanical, ultrasonic, and optical space digitizers for instruments in the operating room has increased. Use of several cameras to track surgical instruments and other objects in the operating field has been described in the papers by E. R. Cosman. Also, product literature from Radionics, Inc. of Burlington, Mass., carries some description. Commonly, two or more cameras are established to view the operating field. The cameras can be pre-calibrated to determine a reference coordinate system in the operating field in which infrared or optical objects can be tracked in three dimensions. It is common practice to attach LEDs or reflectors on instruments and quantitatively track them with the cameras. The LEDs may be placed in a known orientation relative to the tip and the direction of the instruments. Reference to the patient's anatomy is also made by placing LEDs or reflectors on the patient or on apparatus attached to the patient to follow and correct for patient movement. The instrument relative to the patient's anatomy can be referenced to graphics display of image scan data taken previously or during the surgery. This is done by a registration procedure. The paper by E. R. Cosman carries some description of this process.
Attachment of LED or reflector arrays on an arbitrary surgical instrument has been carried out, and the relationship of the tip of the instrument determined by touching a known point in the camera field and thus in the camera coordinate system.
However, an effective technique for calibrating the tip and direction of an arbitrary surgical probe, instrument, microscope, or other device in the operative field is desirable. A surgical instrument direction is an important quantity during surgery in addition to the tip position of the instrument, and a system and method to determine both the probe direction and the probe tip position is useful in clinical application.